Epilepsy is a condition characterized by recurrent seizures, which are the outward manifestation of excessive and/or hyper-synchronous abnormal electrical activity of neuronal structures of the brain. A seizure occurs when the electrical activity of brain structures or even the whole brain becomes abnormally “synchronized.” This is the operational definition of an epileptic seizure.
A seizure patient may suffer from any combination of different types of seizures. Grand mal seizures are the most common form of epilepsy and are characterized by convulsions with tonic-clonic contractions of the muscles. Absence seizures (previously referred to as “petit mal”) are characterized by a brief and sudden loss of consciousness. The psychomotor form of seizures is characterized by a clouding of consciousness for one or two minutes. A complex partial seizure is characterized by a complete loss of consciousness. The type of seizure experienced is typically dependent upon the portion of the cerebral cortex where hypersynchronous activity is occurring. Many types of seizures generally involve the entire brain, while certain types, such as partial seizures, begin in one part of the brain and may remain local.
Regardless of the type of epilepsy, seizures significantly limit the autonomy of the patient. When hit with a seizure, the patient typically loses some level of control of his/her body. In most cases, seizures occur without prior warning to the patient. As a result, epileptic seizures pose a serious safety hazard to the patient and others surrounding the patient. For example, a patient hit with a sudden seizure while driving a car may endanger the patient's own safety as well as the safety of others. Seizure patients are also exposed to a risk of bodily harm when operating machinery and even in daily activities such as crossing a street or going down stairs. In addition to this safety hazard, each seizure will further damage brain structures often resulting in progressive loss of brain function over time.
Researchers have developed a number of techniques for treating seizure disorders and its symptoms. For example, research has shown that inhibiting (namely, reducing the excitation of neurons) the substantia nigra in the brain increases the threshold for seizure occurrence. Researchers have also found that increasing the activity of neurons in the external Globus Pallidum (GPe) increases inhibition of neurons in the subthalamic nucleus, which in turn inhibits neural activity in the substantia nigra.
Neurosurgeons have also been able to diminish the symptoms of many neural disorders by lesioning certain brain areas. Examples include lesioning the ventral lateral portion of the internal Globus Pallidus and the Vim Thalamus for treating movement disorders. Electrical stimulation of the nervous system has also been used to suppress seizures. Finally, infusion of certain drugs into a region of the brain can affect the excitability of the neurons at the site of infusion as disclosed in U.S. Pat. No. 5,713,923 (Ward et al.) assigned to Medtronic, Inc.
Others have studied the effects of electrically stimulating the vagus nerve as a means of suppressing epileptic activity. It has been observed that stimulation of the vagus nerve with certain parameters caused de-synchronization of the brain's electrical activity in animal models. These concepts were disclosed by Zabara in U.S. Pat. Nos. 4,867,164 and 5,025,807.
Under another approach, researchers have devised algorithms to detect the onset of a seizure. Qu and Gotman reported a system that recognizes patterns of electrical activity similar to a template developed from recording an actual seizure. See H. Qu and J. Gotman, “A Seizure Warning System for Long-term Epilepsy Monitoring”, Neurology, 1995;45:2250–2254. Also, see I. Osario, M. Frei, D. Lerner, S. Wilkinson, “A Method for Accurate Automated Real-time Seizure Detection”, Epilepsia, Vol. 36, Suppl. 4, 1995. In each of these techniques for recognizing the onset of a seizure, the developers employ two processes. The first process is to extract certain features from the signals representing the electrical activity of the brain. Examples of the signal features include the signal power or the frequency spectrum of the signals. The second process is to recognize a pattern or set of values for those features that characterize a brain state that will reliably lead to a seizure.
Using pattern recognition techniques, closed-looped protocols for responding to the onset of an epileptic seizure have also been suggested. For example, U.S. Pat. Nos. 6,128,538 and 6,134,474 report closed-loop systems for identifying and responding to a neurological disease, such as epilepsy. These systems, however, identify and respond to neurological events that have already begun. Once started, these events may be difficult to correct. Therefore, a need for more efficient and effective treatments of neurological events continues to exist. Table 1 lists documents that disclose systems and methods that provide for seizure detection.
TABLE 1U.S.Pat. No.InventorsTitle4,867,164ZabaraNeurocybernetic prosthesis5,025,807ZabaraNeurocybernetic prosthesis5,713,923Ward et al.Techniques for treating epilepsy bybrain stimulation and drug infusion6,128,538Fischell et al.Means and method for thetreatment of neurological disorders6,134,474Fischell et al.Responsive implantable system forthe treatment of neurological disordersH. Qu and J. Gotman, “A SeizureWarning System for Long-termEpilepsy Monitoring”, Neurology,1995; 45: 2250–2254I. Osario, M. Frei, D. Lemer,S. Wilkinson, “A Method for AccurateAutomated Real-time Seizure Detection”,Epilepsia, Vol. 36, Suppl. 4, 1995.
All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.